[3A1] Ultrasonic array-based imaging with orthogonal chirps
K Prashar1,2, M Weston1 and B W Drinkwater2
1TWI Wales, UK
2Department of Mechanical Engineering, University of Bristol, UK
Phased Array Ultrasonic Testing (PAUT) is now a widely used method in industry for non-destructive testing. Arrays offer an intuitive view of the interior of a component from which geometric features and defects can be observed. Arrays also offer unprecedented information about the nature and extent of any defects. In recent years, Full Matrix capture (FMC) and Total Focusing Method (TFM) have attracted significant interest due to the high resolution of the images possible throughout an inspection volume. The requirement to transmit on each element separately while receiving on all elements, places a physical limit on the speed of FMC data acquisition. The motivation of this paper is to describe a method to increase speed of data acquisition and imaging whilst maintaining acceptable image quality. A new algorithm which has recently been adopted in the NDT field, Plane-Wave Imaging, is used to accomplish faster scan speeds by firing multiple steered planar waves into the system and receiving on all the elements. To improve speed of acquisition from PWI further, the use of orthogonal linear frequency modulated signals (Linear FM Chirps) is explored. This step allows multiple plane waves, encoded with chirps, to be fired almost simultaneously. The degree of orthogonality, along with other sample parameters such as material attenuation, are shown to determine the balance between the achievable number if image frames per second and the quality of the image. The performance of this method is first explored through simulation where the influence of the key set-up variables is explained. Finally, the technique is shown on a number of industrially relevant samples.
